Do you mean plates at the sides of the blade?
I used some scrap 1/4 mild steel plate roughly 12" square and tack welded them onto the sides of the curved blade (not the cutting edge). I put the blade on the tractor in the "level" position I wanted on my shop floor then 1" tack welded them on place. I can still break them off with a hammer if I ever want to remove them. I also added a pair of gauge wheels on the back in the same "level" position.
I find this does an excellent job of grading my driveway. No side spill. Hydraulic top link gives me excellent grade control with fine levelling, way better than using the 3PH lever.